As is known, there are several different kinds of devices used to detect radiation from celestial objects.
The most common of these devices consist essentially of a parabolic surface made of materials capable of reflecting the radiation concerned (ranging in frequency from a few Ghz to several hundred Ghz), and a receiver positioned at the focus of the parabolic surface.
Using this structure and according to well-known physics laws, the radiation striking the inside surface of the parabolic reflector is reflected at an angle which directs it to the receiving element.
The latter, after detecting the incident radiation, sends corresponding signals containing information about the radiation, to a study centre where the information is analysed and processed.
To capture radiation from different zones in space, prior art parabolic aerials are equipped with drive means designed to vary the angle of the parabolic structure in such a way that its inside surface faces different objects in space.
When the angle of the aerial is varied, however, the parabolic surface is deformed on account of the weight of the aerial's load bearing structure.
Indeed, prior art parabolic aerials are constructed in such a way as to have a nearly perfect parabolic shape at a predetermined angle (usually 45° relative to the ground). When this angle has to be changed, the different components of the structure are subjected to varying gravitational stresses which change the position and angle of the components relative to each other and thus deform the initial parabolic arrangement.
It is evident that this deformation has a negative effect on the receiving performance of the aerial since the incident radiation is no longer directed at the receiving element with the same degree of precision. This means that the intensity of the signal received is greatly reduced (also bearing in mind that the signals come from very distant sources and, therefore, are in themselves very weak).
Moreover, the higher the reception frequency, the greater the negative effect is on the strength of the signal received.
To overcome this problem, prior art teaches the use of active surfaces constructed using a plurality of mobile reflecting surfaces placed side by side in such a way as to form the parabolic structure.
The reflecting elements are usually square or rectangular panels placed edge to edge in such a way as to form a practically uninterrupted surface. By moving the reflecting elements, as explained below, the initial shape of the surface can be maintained practically unchanged, even in the presence of varying gravitational stresses.
The structure is equipped with a plurality electromechanical actuators designed to vary the positions of the reflecting elements in accordance with appropriate control signals.
These actuators consist of an electric motor, usually a DC motor, and a piston, driven by the motor, that moves in the direction defined by the longitudinal extension of the piston itself. The upper end of each piston is connected to one or more reflecting elements whose positions are thus varied by the action of the motor.
The system that controls these movements through the aforementioned control signals includes a processing unit that generates the control signals by which the extent of the movement that each piston must perform (to position the reflecting elements) is communicated to each actuator in order to compensate for the deformation of the active surface due to gravitational stresses.
Thus, whatever the angle of the aerial, the reflecting elements can adjust their positions in such a way that the inside surface of the structure retains the ideal shape at all times, that is to say, a shape which is substantially that of a paraboloid of revolution whose curvature is appropriately adapted to improve the receiving performance of the apparatus.
A major disadvantage of systems such as that just described lies in the fact that all the actuators are directly connected to the processing unit and are directly addressed by the processing unit every time the reflecting elements need to be repositioned. In other words, once the processing unit has selected from its internal table the displacements required for each actuator, it sequentially selects the outputs by which it is connected to the actuators and, through these, transmits the necessary information to each actuator.
A solution of this kind necessarily involves the use of an inordinate quantity of cables since the direct connection of all the actuators to the processing unit requires several dozens of kilometers of cables (up to as much as around 160 km of cables for aerials 100 metres in diameter).
Moreover, the use of cables of considerable length to transmit signals directly to the processing unit of each single motor may contribute to the creation of significant RF interference between the control signals themselves, thus preventing not only the correct operation of the entire adjustment system but also the proper reception of weak radio astronomic signals.